To flap or not to flap: comparison between flapping and clapping propulsions

2017 ◽  
Vol 822 ◽  
Author(s):  
Nathan Martin ◽  
Chris Roh ◽  
Suhail Idrees ◽  
Morteza Gharib
Keyword(s):  
Duty Cycle ◽  
Reynolds Numbers ◽  
Input Power ◽  
Sweep Angle ◽  
Propulsion Mechanism ◽  
Sweep Time ◽  
High Flexibility ◽  
Tip Velocity

A comparison between swimming by flapping and by periodic contractions is conducted. Swimming by flapping is approximated as a pitching plate while swimming by periodic contractions is approximated as clapping plates. A direct comparison is made between the two propulsion mechanisms by utilizing a machine that can operate in either a flapping or a clapping mode between Reynolds numbers of 1880 and 11 260 based on the average plate tip velocity and span. The average thrust generated and the average input power required per cycle are compared between cases where the total sweep angle and the total sweep time are identical. Variation of the kinematics results in a similar thrust between the two mechanisms, but a greater power is required for clapping. Variation of the flexibility results in a consistent decrease in the required power for clapping and a decrease in thrust at high flexibility. Variation of the duty cycle for clapping rigid plates results in a significant increase in thrust and a significant decrease in the required power. Overall, the results suggest that flapping propulsion is the more effective propulsion mechanism within the range of Reynolds numbers tested.

Two-photon excitation microscopy in cellular biophysics

1995 ◽  
Vol 53 ◽  
pp. 62-63
Author(s):  
David W. Piston ◽  
Brian D. Bennett ◽  
Robert G. Summers
Keyword(s):  
Confocal Microscopy ◽  
Laser Beam ◽  
Duty Cycle ◽  
Excited Electronic State ◽  
Input Power ◽  
Two Photon ◽  
Simultaneous Absorption ◽  
Photon Excitation ◽  
Very High ◽  
Two Photon Excitation

Two-photon excitation microscopy (TPEM) provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging and photochemistry. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10-5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Development of a three-dimensional free shear layer

1998 ◽  
Vol 369 ◽  
pp. 49-89 ◽  
Author(s):  
A. J. RILEY ◽  
M. V. LOWSON
Keyword(s):  
Shear Layer ◽  
Flow Instability ◽  
Delta Wing ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Transition To Turbulence ◽  
Free Shear Layer ◽  
Velocity Data ◽  
Sweep Angle ◽  
Vortical Structures

Experiments have been undertaken to characterize the flow field over a delta wing, with an 85° sweep angle, at 12.5° incidence. Application of a laser Doppler anemometer has enabled detailed three-dimensional velocity data to be obtained within the free shear layer, revealing a system of steady co-rotating vortical structures. These sub-vortex structures are associated with low-momentum flow pockets in the separated vortex flow. The structures are found to be dependent on local Reynolds number, and undergo transition to turbulence. The structural features disappear as the sub-vortices are wrapped into the main vortex core. A local three-dimensional Kelvin–Helmholtz-type instability is suggested for the formation of these vortical structures in the free shear layer. This instability has parallels with the cross-flow instability that occurs in three-dimensional boundary layers. Velocity data at high Reynolds numbers have shown that the sub-vortical structures continue to form, consistent with flow visualization results over fighter aircraft at flight Reynolds numbers.

Investigation of New Geometries for High Duty Cycle Far-Infrared p-Type Germanium Lasers

1999 ◽  
Vol 607 ◽  
Author(s):  
Danielle R. Chamberlin ◽  
Erik Bruendermannw ◽  
Eugene E. Haller
Keyword(s):  
Electric Field ◽  
Duty Cycle ◽  
Pulse Length ◽  
Far Infrared ◽  
Contact Geometry ◽  
Input Power ◽  
High Resistivity ◽  
Field Uniformity ◽  
P Type ◽  
Planar Contact

AbstractWe report on increasing the pulse length and repetition rate of p-type germanium lasers through miniaturization, increased electric field uniformity, and improved cooling. We have recently demonstrated that it is possible to improve the electric field uniformity necessary for an efficient laser and at the same time decrease the electrical input power by using a geometry with d/L>>1, where d is the distance between electrical contacts and L is the length in the direction of the Hall field. In order to achieve good heat sinking along with a large d/L ratio, we have developed a new, planar contact geometry. Attaching an undoped, high-resistivity, single-crystal Si heat sink to the base of the Ge planar contact laser increases the duty cycle by a factor of 5.5. In order to further decrease the input power by decreasing the volume of laser crystals in the planar contact geometry, we show as a proof-of-concept the use of polished strontium titanate single crystals as electrically insulating far-infrared mirrors based on restrahl band reflection. The physical phenomena underlying these improvements in this novel geometry will be discussed.

scholarly journals Achieving high input power factor for DCM Buck PFC converter by variable Duty-Cycle control

2019 ◽  
pp. 185-199
Author(s):  
A. Hakeem Memon ◽  
M. Osama Nizamani ◽  
Anwar A. Memon ◽  
Zubair A. Memon ◽  
Amir M. Soomro
Keyword(s):  
Power Factor ◽  
Duty Cycle ◽  
Input Power ◽  
High Input ◽  
High Input Power

Active Control of Flow Separation in a Radial Blower

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
David Greenblatt ◽  
Guy Arzuan
Keyword(s):  
Pressure Rise ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Input Power ◽  
Maximum Pressure ◽  
Proof Of Concept ◽  
Periodic Excitation ◽  
Separated Shear Layer ◽  
Reduced Frequency ◽  
Blower Performance

An experimental investigation was undertaken as a proof-of-concept study for active separation control in a radial blower. Acoustic perturbations were introduced into the impeller housing of a small radial blower with fully stalled blades. Increases in the plenum pressure of 35% were achieved and, based on tuft-based flow visualization, it was concluded that the pressure increases were brought about due to excitation and deflection of the leading-edge separated shear layer. Within the parameter range considered here, the optimum dimensionless control frequencies were found to be O(0.5), irrespective of the blade orientation or number of blades. Moreover, the maximum pressure rise was achieved with an investment of only 2% of the fan input power. Backward bladed impeller blades exhibited slightly larger increases in pressure coefficients when compared with their forward bladed counterparts. The dependence of blower performance on reduced frequency was remarkably similar to that seen on flat plate airfoils at similar Reynolds numbers under periodic excitation.

Innovative Switching Sequences for Sensorless Capacitor Voltage Balancing of Three-Phase NPC Rectifier

2014 ◽  
Vol 15 (1) ◽  
pp. 1-11
Author(s):  
Nitin Langer ◽  
Abdul Hamid Bhat ◽  
Pramod Agarwal
Keyword(s):  
Duty Cycle ◽  
Sampling Period ◽  
Input Power ◽  
Critical Parameters ◽  
Voltage Balancing ◽  
Switching Losses ◽  
Three Phase ◽  
Mode Of Operation ◽  
Innovative Idea ◽  
And Inversion

Abstract This paper presents a modulation strategy for self-balancing of capacitor voltages of three-phase neutral-point clamped bi-directional rectifier (without feedback controller and sensors). It is identified that regions within a sector are divided into two categories: (a) One small vector among three selected vectors and (b) Two small vectors among three selected vectors. For category (a) positive and negative commutation state of small vector is implemented for equal duty cycle but for category (b) positive and negative commutation state of small vectors is implemented for unequal duty cycle. Based on this observation, an innovative idea is executed to remove these discrepancies. The innovative optimized space vector switching sequences negative and positive commutation state of both the small vectors are implemented for equal duty cycle during each sampling period resulting in self-balancing of DC-bus capacitors with much reduced ripples under steady-state and dynamic load conditions for both rectification and inversion mode of operation. The converter exhibits excellent performance in terms of other critical parameters like unity input power factor, low input current THD, minimum possible switching losses, reduced-rippled and well-regulated DC voltage. The proposed control algorithm is tested through exhaustive simulation of converter using MATLAB Simulink software.

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